Numerous types of vascular graft substitutes have been produced in the last four decades. These vascular graft substitutes have included large and small diameter vascular, blood carrying tubular structures, grafts containing valvular structures (vein substitutes, and heart valve substitutes) and lacking valvular structures (artery substitutes). The materials out of which these vascular grafts have been constructed have included man-made polymers, notably Dacron and Teflon in both knitted and woven configurations, and non-man-made polymers, notably tissue engineered blood vessels such as described in U.S. Pat. Nos. 4,539,716; 4,546,500; 4,835,102; and blood vessels derived from animal or human donors such as described in U.S. Pat. Nos. 4,776,853; 5,558,875; 5,855,617; 5,843,181; and 5,843,180.
The prior art processing methods are prohibitively time consuming, easily requiring numerous days, for example anywhere from eight to twenty-one days total processing time. Such long processing times result in proteolytic degradation of the matrix structures of the processed tissues. Over the past few decades numerous efforts have been made to manage the large surgical use of vascular prostheses in the treatment of vascular dysfunctions/pathologies. While vascular prostheses are available for clinical use, they have met with limited success due to cellular and immunological complications, and the inability to remain patent and function. These problems are especially pronounced for small diameter prostheses, i.e. less than about 6 mm. Efforts have been directed at removing those aspects of allograft and xenograft vascular prostheses that contribute to immunological “rejection” and these efforts have focused primarily on development of various “decellularization” processes, which processes require unduly burdensome incubation times. In addition the prior art methods involve using volumes of processing solutions which do not lend themselves to the production of large numbers of vascular grafts, which ability to “scale-up” is necessary for economic clinical use.
The inventive process produces acellular grafts including but not limited to ligaments, tendons, menisci, cartilage, skin, pericardium, dura mater, fascia, small and large intestine, placenta, veins, arteries, and heart valves. The process is advantageous over prior art processes in that processing times and conditions have been optimized and reduced, and the economics of production have been dramatically improved, resulting in large numbers of uniform, non-immunogenic grafts being produced. The grafts produced are non-immunogenic, are substantially free from damage to the matrix, and are substantially free from contamination including for example free from infectious agents.
The invention involves the use of an anionic agent, for example sodium dodecylsulfate (SDS), for the treatment of tissues with the dual objective of decellularization and treatment of tissues to restrict recellularization. Further, the invention expands on the process of treating tissue(s) with SDS, describing how the amount(s) of SDS deposited in the tissue(s) can be further enhanced/reduced to either further inhibit recellularization of the tissue OR enhance recellularization of the tissue. Treatment of tissues with salt solutions prior to treatment with SDS results in different patterns of SDS deposition/precipitation in the tissues than treatment of tissues with SDS followed by treatment of tissues with salt solutions. Treatment of tissues with SDS prior to salt treatment can be expected to result in significant binding of SDS, primarily via hydrophobic interactions, to matrix “proteins” with further deposition of SDS in the tissues as salt precipitated materials by salt precipitation post SDS treatment. Treatment of tissues with salt solutions prior to treatment with SDS solutions can be expected to result in significant precipitation of SDS as a salt precipitated form and less SDS being bound to tissue matrix structure(s) via hydrophobic interactions. It is further understood that the particular salt solution used, either prior to or following SDS treatment, can significantly alter the subsequent solubility of the salt precipitated SDS and thus long-term retention of SDS in the tissues post implantation. The observed salt effects on both precipitability of SDS and subsequent resolubilization of the salt precipitated form of SDS indicate an activity order of Ca>Mg>Mn>K>Na and calcium salts of dodecylsulfate (CaDS) are less soluble and thus more slowly released from treated tissues than, for example, sodium salts of dodecylsulfate (SDS). The invention is directed at a process for producing acellular soft-tissue implants including vascular grafts, veins, arteries, and heart valves, where processing times and conditions have been optimized to dramatically improve on the economics of production as well as to produce a graft with minimum damage to the matrix structure of the acellular graft. It is a further objective of the present invention to describe how to control the amount(s) of anionic detergents, for example sodium dodecylsulfate (SDS), deposited in the tissue(s) with the objective of enhancing or restricting subsequent recellularization.